Equipment for injecting a gas into a cesspool

ABSTRACT

A floating equipment, for injection of a gas into liquid effluents or waste water, and more particularly of a gas rich in oxygen into a basin from the surface, comprising the following elements:
         a driving device, intended to be disposed over the liquid, provided with a vertical output shaft ( 8 ), equipped at its end with a propeller ( 6 ) immersed in the liquid   a pre-mixing device ( 5 ) comprising an injection device ( 7 ) positioned above or below a mobile aerator ( 9 ) with inclined blades, the propeller being situated at the end of the shaft, under the pre-mixing reactor.

CROSS REFERENCE TO RELATED APPLICATIONS

This continuation application claims the benefit of priority under 35U.S.C. §120 to U.S. patent application Ser. No. 14/119,958 filed Nov.25, 2013, which is a 371 of International PCT ApplicationPCT/FR2012/051114 filed Nov. 25, 2013 which claims priority to FrenchPatent Application No. 1154543 filed May 25, 2011, the entire contentsof which are incorporated herein by reference.

BACKGROUND

The present invention concerns the field of equipment enabling theinjection of a gas into liquid effluents or waste water. It is notablyrelevant to methods of aerating biological basins in which sludge isactivated by injection of a gas rich in oxygen or mixtures includingCO₂.

SUMMARY

One of the objectives of the present invention is to propose novelfloating equipment enabling optimization of the energy consumption ofthe device at the same time as eliminating the constraints ofpresent-day equipment.

It will be remembered that aerobic biological treatment of effluentsgenerally consists of bringing those effluents into contact with abiomass (microorganisms) that degrades the pollution contained thereinby transforming the organic molecules. Thus it is known to inject a gas,generally an oxygenated gas, into the effluents contained in a basin, insuch a manner as to feed the biomass. To this end, numerous devices forinjecting gas into the effluents are offered on this market. Most of thesystems are either immersed or floating.

They generally also agitate the effluents, the injection of theoxygenated gas combined with the agitation enabling better dissolutionof the oxygenated gas in the effluent. This dissolution is measured bythe transfer capacity of the device. For most of these devices foragitation of the liquid and injection of gas into the liquid, part ofthe transfer of the gas into the liquid is effected by gas/liquid mixingmeans, such as a venturi or a turbine, forming an emulsion of the gas inthe liquid, and the rest of the transfer is obtained at the time ofdispersion of the emulsion in the liquid.

It has been observed that most of these agitation and injection deviceshave had a limited injection capacity: beyond a certain gas injectionflow rate, the device gets blocked because, at the level of the means ofinjection of the gas into the liquid, the volume of gas becomes toolarge relative to the volume of liquid. While it would be possible totransfer and dissolve more gas in the liquid contained in the treatmentbasin, the device cannot provide the whole quantity of gas necessary.

Floating systems enabling aeration by injection of a gas rich in oxygenuse relatively complex technologies leading to costly constraints onmanufacture and use and consequently limiting their use.

There may be cited by way of illustrative example the document EP-995485 A1, which describes floating equipment that enables transfer of agas rich in oxygen into a basin with a very high transfer efficiency.However, it uses for this purpose a complex technology calling on aturbine enabling a gas/liquid emulsion to be created, complemented bysystems enabling this emulsion to be directed toward a propellerdesigned to disperse this emulsion in the basin.

The combination of such elements, turbine, systems enabling direction ofthe gas/liquid emulsion and dispersion propeller, has the following mainconsequences:

-   -   High energy consumption, the turbine consuming approximately 40%        of the total energy consumed by the equipment;    -   High equipment weight, implying a high material cost and        constraints on the choice of floats;    -   Manufacture and assembly constraints having the consequence of        high equipment manufacture and maintenance costs;    -   A limit on the flow rate of gas that may be injected by the        equipment (see above), caused in particular by the use of a        turbine and systems enabling direction of the gas/liquid        emulsion generated by the turbine.

Thus one of the objectives of the present invention is to proposefloating equipment enabling the injection of a gas rich in oxygen andhaving a gas transfer efficiency equivalent to the prior art deviceswhilst limiting or eliminating the technical drawbacks of those priorart devices.

To achieve this objective, it is proposed here to eliminate the turbine,with the aim of achieving the following objectives:

-   -   a reduction of approximately 30% in the energy consumed;    -   the elimination of the main elements for guiding the flows        generated by the turbine;    -   an increase in the blocking limit of the equipment of more than        50%;    -   a reduction of approximately 25% in the weight of the equipment;    -   major simplification of its manufacture, assembly and        maintenance;    -   a reduction in manufacturing and maintenance costs;    -   an increase in the field of action of the equipment for        equivalent consumed power.

Eliminating the turbine could nevertheless appear negative to the personskilled in the art since it has the consequence of eliminating wantedfunctions such as the generation of fine bubbles (typically in the range0.8 to 2.5 mm in size) or the transfer rate of part of the gas.

As explained in more detail hereinafter, the proposed novel equipment ofthe present invention has been designed to replace or compensate thesebasic functions and to this end combines the following elements:

-   -   a driving device, intended to be disposed over the liquid,        provided with a vertical output shaft, equipped at its end with        a propeller immersed in the liquid, the propeller preferably        being characterized by a high coverage rate (see below);    -   a device that might be called a reactor of the pre-mixing type        comprising an injection device (for example an injection torus),        positioned above or below a mobile aerator with inclined blades;    -   the propeller is situated at the end of the shaft, below the        pre-mixing reactor.

The expression “coverage rate” as applied to the propeller means theratio of the area covered by the blades and the area of the circlewithin which the propeller is inscribed.

As stated above, the equipment includes an injection device, which ispreferably a torus provided with a number of orifices designed forregular diffusion of the gas positioned in a circle inscribed in thediameter of the propeller. Studies carried out by the Applicant havedemonstrated the advantageous performance of the injection torus inachieving homogeneous diffusion of the gas, but also in reducingpossible phenomena of clogging, favouring easy installation and reducedmaintenance. The orifices of the torus are preferably directed downwardto prevent possible clogging.

Although the torus is preferred in accordance with the invention, it isequally possible to envisage, without departing from the scope of theinvention, using other injection devices such as porous elements ofdifferent shapes (plates, candle filters or micro-perforated plates,etc.).

The basic functions of the reactor are obtained by combining a diffuserand a mobile aerator within inclined blades, judiciously positionedrelative to the other elements of the equipment and notably thedispersion propeller. The hydraulic flow generated by this combinationand this positioning lead to an optimized flow in the reactor. The“diffuser and mobile aerator with inclined blades” pair provides thepre-mixing reactor function indispensable to achieving the requiredperformance, the choice, the combination and the positioning of thevarious elements constituting the overall equipment ensuring on the onehand the production of the pre-mix and on the other hand its dispersionin the basin, enabling optimum transfer into the basin to be obtained.

The arrangement proposed by the invention enables the pre-mix comingfrom the pre-mixer to be diffused in an area in which the liquid speedfield is the optimum from the point of view of its intensity and itsdirection, in order to propel the bubbles as far as possible and toprevent the phenomenon of coalescence.

The person skilled in the art might be equally surprised by the presencein the equipment of the present invention of a mobile aerator withinclined blades.

A mobile aerator with inclined blades is not generally used in thedispersion of gas in liquids.

Nevertheless, in the case of the invention, this use is possible andfavourable because of the use of a propeller with a high coverage rateand because of the positioning of said mobile aerator within the variouscomponents.

Thus it has been possible to demonstrate that the mobile aerator withinclined blades generates:

-   -   An axial and radial flow favouring the homogeneity of the        reactional mixture;    -   Small gas bubbles (because of a high shear coefficient of the        mobile aerator);    -   Low disturbance of the hydraulic flow of the equipment, produced        mainly by the propeller.

The mobile aerator with inclined blades is also characterized by areduced energy consumption compared to the mobile aeratorsconventionally used for this function.

To summarize, there are found in this technical field only mobileaerators with straight blades, producing only a purely radial flow, thuscreating a higher resistance, and thereby a higher energy consumption.

Thus the present invention concerns floating equipment, for injection ofa gas into liquid effluents or waste water, and more particularly of agas rich in oxygen into a basin from the surface, comprising thefollowing elements:

-   -   a driving device, intended to be disposed over the liquid,        provided with a vertical output shaft, equipped at its end with        a propeller immersed in the liquid;    -   a pre-mixing device comprising an injection device (for example        an injection torus), positioned above or below a mobile aerator        with inclined blades, the propeller being situated at the end of        the shaft, under the pre-mixing reactor.

The invention may furthermore adopt one or more of the followingfeatures:

-   -   the propeller has a pumping flow rate number N_(Qp) that is in        the range 0.3 to 1, where:    -   Q_(p)=N_(Qp)×N×D³; where Q_(p) is the pumping flow rate of the        propeller, N the rotation speed of the propeller, and D the        diameter of the propeller;    -   the injection device is a torus, provided with injection        orifices, and positioned in a circle inscribed in the diameter        of the propeller, the torus being positioned at a distance in        the range 0.01 to 1.5 times the diameter of the propeller above        the propeller, preferably at a distance in the range 0.03 to 0.3        times the diameter of the propeller, above the propeller;    -   the injection device is a torus, provided with injection        orifices, the torus having a diameter of between 20 to 200% of        the diameter of the propeller, advantageously 30 to 120% of the        diameter of the propeller;    -   the injection device is a torus, provided with injection        orifices, the internal space of the torus being        compartmentalized into at least two separate zones able to be        supplied with different gases.

By way of example it is possible to supply one of the zones of the toruswith oxygen and the other one or one of the other zones with a mixtureof O₂/O₃. The possibility of having different gases (O2/O2+O3, O2/air,O2 or air/CO2 etc.) or supplying by means of a gas of different qualityis particularly advantageous for some applications. Thus by way ofexample it is possible to consider the injection of air and oxygen in asimultaneous or alternative manner by eliminating any safety risk byusing completely separate networks (no risk of contaminating the oxygenline with poor quality air, no risk of oxygen returning towards to theair compressors etc.).

It is also possible to consider using the same equipment for theinjection of CO₂ in the context of regulating the pH and at the sametime or in an alternative manner to inject a gas comprising oxygen forperforming aeration.

In the context of gases with different flow rates/pressures problemsassociated with controlling the pressure and the flow rate relative toone another are eliminated:

-   -   in one variant the injection device is formed by two        half-toruses, each half-torus being able to be supplied with        different gases as already described above,    -   the injection device is formed by an assembly of porous elements        of the porous candle filter type or porous plate type or        perforated plate type, preferably 3 in number and situated in a        volume defined by a vertical cylinder centered on the vertical        axis of the propeller having an outside diameter preferably        equal to at least 3 times the diameter of the propeller and a        height preferably equal to at least three times the diameter of        the propeller;    -   the distance between the lower face of the float and the upper        leading edge of the propeller is in the range 0.5 to 1.5 times        the diameter of the propeller, preferably in the range 0.8 to        1.0 times the diameter of the propeller;    -   the distance between the injection torus and the mobile aerator        with inclined blades is in the range 1 to 20% of the diameter of        the mobile aerator, preferably close to 2.5% of the diameter of        the mobile aerator;    -   the mobile aerator with inclined blades includes 2 to 12 blades,        preferably 4 to 8 blades, and preferably an even number of times        the number of blades of the propeller situated at the end of the        shaft;    -   the mobile aerator with inclined blades is positioned below the        injector at a distance in the range of 5 mm to 100 mm;    -   the injected gas is a gas with an oxygen content in the range 25        to 100%, or an ozone-containing gas, or a carbon        dioxide-containing gas the CO₂ content of which is in the range        5 to 100%, or a gas comprising 80 to 100% nitrogen.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will emerge from thefollowing description of embodiments given by way of non-limitingexamples and with reference to the appended drawings, in which:

FIG. 1 is a partial diagrammatic sectional view showing one embodimentof the equipment of the invention using torus-type injection means;

FIG. 2 shows an embodiment of a mobile aerator with inclined blades ofthe invention including 6 blades.

FIG. 3 is a detailed view of one of the embodiments of the inventioncomprising anti-vibration plates.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows, in floating equipment, for the injection of a gas into abasin 1 of liquid effluents or waste water according to the invention:

-   -   a driving device, intended to be disposed over the liquid 1,        provided with a vertical output shaft 8, equipped at its end        with a propeller 6 immersed in the liquid;    -   the apparatus floats thanks to the presence of one or more        floats 3;    -   a pre-mixing device 5 comprising a torus-shaped injection device        7 (supplied by the gas inlet 2), positioned above a mobile        aerator 9 with inclined blades, the propeller being situated at        the end of the shaft, under the pre-mixing reactor. The        embodiment shown here illustrates the case of a torus 7, the        internal space of which is continuous, non-compartmentalised and        supplied with gas via the single inlet 2, but a person skilled        in the art would understand that, in the case of a        compartmentalized torus with an internal space compartmentalized        into at least two separate zones and able to be supplied with        different gases, two or more gas inlets 2 would be provided on        the torus;    -   in the embodiment represented, the number of blades of the        propeller is 3, and the number of blades of the mobile aerator        is 6;    -   a system 4 of counter-blades, here for the embodiment shown the        device comprises 3 counter blades), enabling on the one hand the        delimitation of the pre-mixing area but also preventing the        formation of vortices and driving the equipment in rotation (the        equipment would then turn like a spinning top). This system of        counter-blades moreover enables orientation of the axial flow.

FIG. 1 is only a partial diagrammatic representation of the equipmentwhich does not show all of the secondary or optional details in order toshow the essential elements which belong to the invention more clearly,and thus in particular the metal body of the assembly has not been shownwhich are traditionally joined to the constituent elements of suchinjection equipment, and for example here the floats, the torus or eventhe counter blades. Thus FIG. 1 shows two reinforcing bars 10 connectingthe two counter blades 4, said bars forming part of such a body.

FIG. 3 illustrates in a detailed view one of the advantageous modes ofimplementing the invention which can be found in very interestingconfigurations, and in particular can limit the vibrations of thedevice. In this advantageous mode, the device comprises plates 11 with aparallelepiped or trapezoidal form, here three in number (one plate percounter blade), said plates fixed at one end to the body 10, for exampleon one of the counter blades 4 (they even form part of such a body),plates directed towards the drive axis of the propeller, and on theother hand located below the waterline.

Without being restricted in any way by the following technicalexplanations the Applicants have suggested that such a configurationpartially channels the flow of liquid suctioned by the propeller and cancontribute to a reduction in the potential vibration of the system.

Equipment like that described in the context of FIGS. 1 and 2 has beenused for the injection of oxygen into a biological oxidation basintreating effluents from a paperwork.

For an oxygen demand evaluated at 53.3 kg/h, a flow rate of oxygen of 45m³/h was injected into the basin. The calculated transfer efficiency wasevaluated at a value close to 91.3%, which represents excellentperformance.

Thus it has been demonstrated that simplification of the equipment hasnot degraded the performance obtained, to the contrary.

While the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives,modifications, and variations will be apparent to those skilled in theart in light of the foregoing description. Accordingly, it is intendedto embrace all such alternatives, modifications, and variations as fallwithin the spirit and broad scope of the appended claims. The presentinvention may suitably comprise, consist or consist essentially of theelements disclosed and may be practiced in the absence of an element notdisclosed. Furthermore, if there is language referring to order, such asfirst and second, it should be understood in an exemplary sense and notin a limiting sense. For example, it can be recognized by those skilledin the art that certain steps can be combined into a single step.

The singular forms “a”, “an” and “the” include plural referents, unlessthe context clearly dictates otherwise.

“Comprising” in a claim is an open transitional term which means thesubsequently identified claim elements are a nonexclusive listing (i.e.,anything else may be additionally included and remain within the scopeof “comprising”). “Comprising” as used herein may be replaced by themore limited transitional terms “consisting essentially of” and“consisting of” unless otherwise indicated herein.

“Providing” in a claim is defined to mean furnishing, supplying, makingavailable, or preparing something. The step may be performed by anyactor in the absence of express language in the claim to the contrary.

Optional or optionally means that the subsequently described event orcircumstances may or may not occur. The description includes instanceswhere the event or circumstance occurs and instances where it does notoccur.

Ranges may be expressed herein as from about one particular value,and/or to about another particular value. When such a range isexpressed, it is to be understood that another embodiment is from theone particular value and/or to the other particular value, along withall combinations within said range.

All references identified herein are each hereby incorporated byreference into this application in their entireties, as well as for thespecific information for which each is cited.

What is claimed is:
 1. A floating equipment, for injection of a gas intoliquid effluents or waste water, comprising the following elements: adriving device, intended to be disposed over the liquid, provided with avertical output shaft (8), equipped at its end with a propeller (6)immersed in the liquid; and a pre-mixing device (5) comprising aninjection device (7) positioned above or below a mobile aerator (9) withinclined blades, the propeller being situated at the end of the shaft,under a pre-mixing reactor, wherein the injection device is of torusshape and is formed by an assembly of porous elements.
 2. The equipmentof claim 1, wherein the assembly of porous elements is of porous candlefilter type or porous plate type or perforated plate type.
 3. Theequipment of claim 2, wherein the porous elements are situated in avolume defined by a vertical cylinder centered on the vertical axis ofthe propeller, the vertical cylinder having an outside diameter equal toat least 3 times the diameter of the propeller and a height equal to atleast three times the diameter of the propeller.
 4. The equipment ofclaim 1, wherein the propeller has a pumping flow rate number NQp thatis in the range 0.3 to 1, where: Qp=NQp×N×D3; where Qp is the pumpingrate of the propeller, N the rotation speed of the propeller, and D thediameter of the propeller.
 5. The equipment of claim 1, wherein theinjection device is a torus, and positioned in a circle inscribed in thediameter of the propeller, the torus being positioned at a distancebetween 0.01 to 1.5 times the diameter of the propeller above thepropeller.
 6. The equipment of claim 1, wherein the injection device isa torus, and positioned in a circle inscribed in the diameter of thepropeller, the torus being positioned at a distance between 0.03 to 0.3times the diameter of the propeller, above the propeller.
 7. Theequipment of claim 5, wherein the distance between the injection torusand the mobile aerator with inclined blades is between 1 to 20% of thediameter of the mobile aerator.
 8. The equipment of claim 5, wherein thedistance between the injection torus and the mobile aerator withinclined blades is close to 2.5% of the diameter of the mobile aerator.9. The equipment of claim 1, wherein the injection device is a torus,the torus having a diameter between 20 to 200% of the diameter of thepropeller.
 10. The equipment of claim 1, wherein the injection device isa torus, the torus having a diameter between 30 to 120% of the diameterof the propeller.
 11. The equipment of claim 1, wherein said equipmentfloats thanks to the presence of one or more floats (3) and in that thedistance between the lower face of the float and the upper leading edgeof the propeller is between 0.5 to 1.5 times the diameter of thepropeller.
 12. The equipment of claim 1, wherein said equipment floatsthanks to the presence of one or more floats (3) and in that thedistance between the lower face of the float and the upper leading edgeof the propeller is between 0.8 to 1.0 times the diameter of thepropeller.
 13. The equipment of claim 1, wherein the mobile aerator withinclined blades includes an even number of times the number of blades ofthe propeller situated at the end of the shaft.
 14. The equipment ofclaim 1, wherein the mobile aerator with inclined blades includes 2 to12 blades.
 15. The equipment of claim 1, wherein the mobile aerator withinclined blades includes 4 to 8 blades.
 16. The equipment of claim 1,wherein the mobile aerator with inclined blades is positioned below theinjection device at a distance of between 5 mm to 100 mm from thatinjection device.